The present invention relates to a wideband receiver, referred to as a so-called scanner, and more specifically, relates to a wideband receiver and a channel scanning method, which can detect a channel at a higher speed.
A wideband receiver which scans a wide frequency band, detects a channel appearing in the frequency band, and according to circumstances, demodulates a signal in the detected channel, and outputs this signal as an acoustic signal has heretofore been known. As shown in FIG. 1, such a wide band receiver comprises, in general, an antenna 12, an RF amplifier 14, a frequency converter 16, a frequency synthesizer 18 consisting of a PLL (Phase Locked Loop) circuit and a voltage controlled oscillator (VCO), a narrow-band filter 102, a detector 104, a control circuit 106 and a demodulation circuit 108.
Radio wave received by the antenna 12 is converted to an intermediate frequency signal by the frequency converter 16 via the RF amplifier 14. This intermediate frequency signal is provided to the detector 104, through the narrow-band filter 102 substantially having a frequency bandwidth, that is, a step width. The detector 104 detects whether a communication signal is included or not in the signal having passed through the narrow-band filter 102, and outputs a detection signal indicating the detection of the communication signal to the control circuit 106. The control circuit 106 responds to, for example, the detection signal, fixes the frequency of the local oscillation signal from the frequency synthesizer 18, controls each circuit so that the detected communication signal is output to the demodulation circuit 108, or changes the frequency of the local oscillation signal, and controls each circuit so that an intermediate frequency signal having other frequency is output from the frequency converter 16.
In this manner, by repeating a processing in which the frequency of the intermediate frequency signal is changed, and a narrow-band filter having a predetermined frequency bandwidth (channel width) filters this signal, and it is detected whether a communication signal is included or not in the filtered signal, signals in communication included in the search frequency range to be searched are detected, and one of these signals can be output in speech or the like.
In the conventional wideband receiver, however, it is required to execute changes of the frequency of the local oscillation signal by the number of channels included in the search frequency range, that is, by (search frequency range/channel width) times. For example, when aeronautical radio having a search frequency range of from 108 MHz-136 MHz, and a frequency bandwidth, i.e., channel width of 25 kHz is to be detected, it is necessary to change the frequency of the local oscillation signal for (24 M/25 k)=960 times. In general, the frequency control time of a frequency synthesizer, that is, the time until the frequency is changed and presence of a predetermined signal is detected is several tens msec. Therefore, iteration of frequency changes and channel search for many times becomes an obstruction in improving the search speed of the receiver.
Moreover, in the conventional wideband receiver, when a certain channel is being detected, it can be only detected whether or not there is a signal in communication in that channel, and the signal in that channel can only be demodulated and output, and detection of a plurality of channels and demodulation and output of a signal at the same time cannot be performed.
It is an object of the present invention to provide a wideband receiver that can detect channels in the search frequency range at a high speed, and can regenerate that signal.
It is another object of the present invention to provide a wideband receiver that can perform detection of a channel and demodulation and output of a signal in that channel or in other channels, at the same time, thereby enabling realization of high-speed search, which is easy to use.
The object of the present invention is achieved by a wideband receiver that receives radio wave, and uses a frequency range allocated to certain broadcasting as a search frequency range to detect a channel being in communication in that search frequency range, comprising: a frequency converter which converts the frequency of a signal input via an antenna, by use of a local oscillation signal from a local oscillator; a wideband filter connected to the frequency converter, which receives the output of the frequency converter to allow a signal component corresponding to a scanning band including a bandwidth of at least a plurality of channels to pass therethrough; an A/D converter connected to the wideband filter, which receives the signal component and converting the signal component to a digital signal; an FFT arithmetic circuit connected to the A/D converter, which receives the digital signal and subjects the signal to a fast Fourier transform; and a detection circuit which detects a channel being in communication in a predetermined scanning band, based on the calculation result by means of the FFT arithmetic circuit; wherein it is constructed such that a frequency of a local oscillation signal is changed to change the scanning band, whereby a channel being in communication is detected in an allocated frequency range.
According to the present invention, a signal corresponding to the scanning band including a bandwidth of a plurality of channels is taken out by a wideband filter. This signal is further subjected to the FFT operation to sequentially calculate a power with respect to the frequency, and a channel being in communication can be detected in the scanning band, by referring to this power. Moreover, according to the present invention, a plurality of channels can be detected by scanning of the scanning band. As a result, the number of times of frequency change of the local oscillation signal and the number of times of frequency transform can be reduced, thereby enabling reduction in the processing time required for scanning of channels.
In a preferred aspect of the present invention, the width of a scanning band of a wideband filter is set to be:
Ibw/Cbw greater than Tfft/Tch+1
(wherein Ibw is a scanning band width, Cbw is a search frequency range, Tfft is time for operation in the FFT arithmetic circuit, and Tch is frequency control time of a local oscillator).
In the above aspect, it is more preferable that the left side in the above expression is sufficiently large.
In the more preferable aspect of the present invention, it is so constructed that the wideband receiver comprises a demodulation circuit connected to the A/D converter, which receives a digital signal and demodulates the signal in the detected channel, so that demodulation of a signal in a predetermined channel is realized in parallel with the operation of the FFT arithmetic circuit.
Alternatively, it may be constructed such that the wide band receiver comprises a demodulation circuit connected to the wideband filter, which receives the output from the wideband filter to demodulate a signal in a predetermined channel, so that demodulation of a signal in a predetermined channel is realized in parallel with the operation of the FFT arithmetic circuit. According to these aspects, it becomes possible to realize detection of a channel and demodulation of the detected channel in parallel, in a certain scanning band.
According to another aspect of the present invention, a wideband receiver that receives radio wave, and uses a frequency range allocated to certain broadcasting as a search frequency range to detect a channel being in communication in the search frequency range, comprises: signal extraction means for extracting a signal corresponding to a scanning band corresponding to a search frequency range, or to a scanning band obtained by dividing the search frequency range into at least two; power calculation means for receiving a signal extracted by the signal extraction means and calculating a power with respect to the frequency; and channel detection means for detecting a channel being in communication in the scanning band, based on the calculation result from the power calculation means, wherein a channel being in communication is detected in the search frequency range by changing the scanning band according to need.
In this aspect, it is possible to detect a plurality of channels in the scanning band, and hence the number of times of changing the scanning band can be reduced, thereby enabling reduction in the processing time for channel scanning.
Moreover, the object of the present invention can be achieved by a method comprising steps for realizing the above construction.